Daughter wants to meet her father

My daughter is 17 and really wants to meet her father. It's a complicated situation because her father is... Not there in the head. It was some hook up from a Halloween party back when I was 16 and everyone knew he was a weird dude, but he's not just weird, he is not sane in anyway shape for form. I don't know how to describe him but a lot of people thought his parents were brother and sister in High school just because of how he is. I never bad mouthed him to her or called him a deadbeat. I was just honest that he isn't okay up there. I guess she just decided she wants to meet him. For that to happen I would have to find where he even is. Last time I heard about him he was in a mental institution. Idk if he's there now and I know she's about to be an adult and should make her own decisions. I just feel she will be disappointed when she meets him. She won't be able to really ask him questions because he just talks complete nonsense, and I feel like she has the image the way it will go and I know she will be disappointed. I want to support her but also don't want her to be disappointed if she can't form a relationship with him. It's not her fault or his. He just isn't capable of being what she thinks a father should be.